1. Field of the Invention
The present invention relates generally to a hydraulic power transmission joint for motor vehicles, for use in the distribution of a driving force to front and rear wheels, and more particularly to a hydraulic power transmission joint cutting off torque without any influence of rotational differences between the front and rear wheels.
2. Description of the Related Arts
Conventional hydraulic power transmission joints are known from e.g., U.S. Pat. Nos. 5,706,658 and 5,983,635. Such a hydraulic power transmission joint is used in a fashion as shown in FIG. 1 for example.
FIG. 1 illustrates an example of a hydraulic power transmission joint being currently developed by the inventors of the present application.
Referring to FIG. 1, a propeller shaft 101 connecting directly with front wheels is coupled too a companion flange 102 to which is coupled the hydraulic power transmission joint generally designated as 122. The hydraulic power transmission joint 122 comprises a housing shank 104 formed with a cam face 103 and fixedly inserted into the inner periphery of the companion flange 102, and a housing 105 secured by welding to the housing shank 104. The housing shank 104 is supported via a front bearing 106 by a differential gear case 107. A main shaft 108 acting as an output shaft connects with a drive pinion gear 109 associated with a rear differential gear. A rotor 110 is fitted via splines to the main shaft 108 and is rotatably housed in the housing 105. The rotor 110 is provided with a plurality of axially extending plunger chambers 111 which accomodate plungers. 112 reciprocatively under a pressing force of return springs 113, with the plungers 112 being operated by the cam face 103 upon the relative rotations between the two shafts. The rotor 110 is formed with an intake/discharge hole 114 leading to the plunger chambers 111. A rotary valive 115 is provided with a discharge port and an intake port (neither of which are shown) which are capable of communicating with the intake/discharge hole 114. The rotary valve 115 has an orifice (not shown) for generating a flow resistance by flow of oil discharged by the displacement of the plungers 112. The rotary valve 115 is further provided with a weight 116 for cutting off torque. A bearing retainer 117 is securely press fitted to the housing 105 and is positioned by a snap ring 118. Needle bearings 119 and 120 are interposed between the bearing retainer 117 and the rotary valve 115 and between the bearing retainer 117 and the main shaft 108, respectively. An accumulator piston 121 is further provided for absorbing thermal expansion and contraction of oil residing within the joint.
Such a hydraulic power transmission joint 122 is arranged as shown in FIG. 2 and generates torque hydraulically as a function of the rotational-speed differences between the front and rear wheels. More specifically, the hydraulic power transmission joint 122 is interposed between a front differential gear 123 and a rear differential gear 124, with the propeller shaft 101 acting as a driving shaft being coupled to the hydraulic power transmission joint 122. The front differential gear 123 is interposed between front driving wheels 125 and 126. The rear differential gear 124 is interposed between rear driven wheels 127 and 128.
In the event that tires having diameters have been mounted on the front driving wheels 125 and 126 and on the rear dirven wheels 127 and 128, the rotational-speed difference of the hydraulic power transmission joint 122 may increase accordingly as the vehicle velocity rises, with the result that torque may increase and accumulate within the front and rear differential gears 123 and 124, adding to the running resistance. In order to solve this problem, as illustrated in FIG. 3, there is proposed a valve which is provided within the hyrdraulic power transmission joint 122 and which has a weight 116 operating depending on the vehicle velocity (centrifugal force) for torque cutoff. More specifically, a rotary valve 115 is spline mounted within the housing 105 connecting directly with the propeller shaft 101, so as to rotate jointly with the housing 105. A weight 116 is provided within the rotary valve 115. In response to the number of rotations (centrifugal force), the weight 116 rotates around its center of rotation in the center of rotation in the direction indicated by an arrow A, so as to open a high-pressure oil drain portion 130 for draining off the high-pressure oil within the plunger chambers. on the vehicle velocity (centrifugal force) for torque cutoff. More specifically, a rotary valve 115 is spline mounted within the housing 105 connecting directly with the propeller shaft 101, so as to rotate jointly with the housing 105. A weight 116 is provided within the rotary valve 115. In response to the number of rotations (centrifugal force), the weight 116 rotates around its center of rotation in the direction indicated by an arrow A, so as to open a high-pressure oil drain portion 130 for draining off the high-pressure oil within the plunger chambers to cut off torque.
Due to such a vehicle velocity (centrifugal force), dependent torque is cutoff by the operation of the weight provided within the hydraulic power transmission joint. However, the weight may work early and cut off the torque even at a low vehicle velocity, e.g., upon the escape from any difficult situations. More specifically, when in stuck, only the front wheels acting as the driving wheel sand the propeller shaft rotate at a higher speed, with the rotary valve 115 connecting directly with the propeller shaft, whereupon the weight 116 may work to cut off the torque transmission to the rear wheel side, making an escape from sandy or muddy spots difficult.
According to the present invention there is provided a hydraulic power transmission joint capable of cutting off torque depending on the vehicle velocity without any influence of rotational differences between front and rear wheels.
The present invention is directed to a hydraulic power transmission joint disposed between a driving shaft and a driven shaft which are capable of relative rotations, for transmitting torque depending on rotational-speed differences between the two shafts. According to a first aspect of the present invention, such a hydraulic power transmission joint comprises
a housing coupled to the driving shaft and having a cam face formed on the inner side of the housing; a rotor coupled to the driven shaft and rotatably housed in the housing, the rotor including a plurality of axially extending plunger chambers; a plurality of plungers each accommodated reciprocatively under a pressing force of a return spring in each of the plurality of plunger chambers, the plurality of plungers being operated by the cam face upon relative rotations between the two shafts; an orifice causing oil discharged by a displacement of the plunger to create a flow resistance to impart a high pressure to the interior of the plunger chamber, the orifice allowing torque transmitted from the housing to the rotor to be generated by a reaction force of the plunger; a valve which when a predetermined number of rotations is reached, operates to cut off torque; and a coupling member for coupling the rotor connecting to the driven shaft and the valve together, the coupling member allowing rotations of the valve to be in synchronism with rotations of the driven shaft.
In this case, the valve may include a weight which when a predetermined number of rotations are reached, rotates around its center of rotation by a centrifugal force to drain off a high-pressure oil residing within the plunger chamber. Preferably, the housing connects with a driving shaft in the form of a propeller shaft extending from a front differential gear, and the rotor connects with an input shaft of a rear differential gear.
According to the present invention having such a configuration, the number of rotations at which the weight works can be determined by the driven shaft associated with the rear wheels by virtue of the coupling member for coupling the rotor connecting with the rear wheel driven shaft and the valve together and due to the synchronism of rotations of the valve with rotations of the rear wheel driven shaft. Thus, it is possible to cut off torque depending on the actual vehicle velocity without being affected by the rotational-speed differences between the front and rear wheels. As a result, torque to be transmitted to the rear wheels is prevented from being cut off, e.g., upon the escape from any difficult situations.
According to a second aspect of the present invention, there is provided a hydraulic power transmission joint disposed between a driving shaft and a driven shaft which are capable of relative rotations, for transmitting torque depending on rotational-speed differences between the two shafts. The hydraulic power transmission joint comprises a housing coupled to the driven shaft and having a cam face formed on the inner side of the housing; a rotor coupled to the driving shaft rotatably housed in the housing, the rotor including a plurality of axially extending plunger chambers; a plurality of plungers each accomodated reciprocatively under a pressing force of a return spring in each of the plurality of plunger chambers, the plungers being operated by the cam face upon relative rotations between the two shafts; an orifice causing oil discharged by a displacement of the plunger to create a flow resistance to impart a high pressure to the interior of the plunger chamber, the orifice allowing torque transmitted from the rotor to the housing to be generated by a reaction force of the plunger; a valve which when a predetermined number of rotations is reached, operates to cut off torque; and a fitting structure for fitting the valve into the interior of the housing connecting to the driven shaft, the fitting structure allowing rotations of he valve to be in synchronism with rotations of the driven shaft.
Herein, the valve may include a weight which when a predetermined number of rotations are reached, rotates around its center of rotation by a centrifugal force to drain off a high-pressure oil residing within the plunger chamber. Preferably, the housing connects with a driving shaft in the form of a propeller shaft extending from a front differential gear, and the rotor connects with an input shaft of a rear differential gear.
In this case as well, the number of rotations at which the weight works can be determined by to rotations of the driven shaft associated with the rear wheels by virtue of the fitting valve into the housing connecting with the rear wheel driven shaft and due to the synchronism of rotations of the valve with rotations of the rear wheel driven shaft. Thus, it is possible to cut off torque depending on the actual vehicle velocity without being affected by the rotational-speed differences between the front and rear wheels. As a result, torque to be transmitted to the rear wheels is prevented from being cut off, e.g., upon the escape from any difficult situations.
The above and other objects, aspects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.